The invention relates to an electromotive adjustment drive which can be operated by a safety voltage, in particular a drive for a piece of furniture, and which is equipped with a control unit operated by a hand-operated device and connected by at least one cable with a voltage source supplied with the mains voltage. Adjustment drives of the type involved here are operated by low-voltage motors having a supply voltage provided by a transformer connected to the electric power grid. The motors may be operated by alternating voltage as well as direct voltage. Safety reasons dictate however that the voltage is decreased substantially. Adjustment drives of standard construction have transformers integrated in the housing of the adjustment drive. As a consequence, the current-carrying cable between the voltage source and the transformer is live. When the adjustment drive is utilized to operate a piece of furniture, many users perceive the presence of live electric or electronic components or component groups in the piece of furniture, e.g. a chair or a bed, as objectionable.
It has therefore been proposed to arrange the transformer outside the housing of the adjustment drive, even in those cases when the available installation space is too small to accommodate the adjustment drive, because the removal of the transformer renders the dimensions of the adjustment drive smaller. Such detached transformers are also called as add-on transformers. Up to a particular output, the transformer may also be configured as power plug so as to be positioned in immediate proximity to a socket receptacle. Furthermore, this configuration has the drawback that the mains voltage is continuously supplied to the transformer. No-load losses are converted into heat, thereby incurring added costs. It has therefore been proposed to separate the transformer from the voltage source through disconnection from the voltage source during the conceivably very long idle period. This, however, entails the drawback that the power disconnection requires for control a particular cable which must be so configured that the mains voltage as well as the control voltage can be applied. Another option would be to lay two different cables; this requires however a complicated insulation so that costs are further increased.
The control unit is typically integrated either in the housing of the adjustment drive or in a housing which is connected to the housing of the adjustment drive. The hand-operated device is normally implemented as a hand switch having several push buttons and outputting signals which are transmitted to the control unit via a cable or also wireless.